The invention relates to a system for the optical detection of a distant object.
Systems for the optical detection of an object are known, for example, from German Patent Documents DE 101 39 237 A1 and DE 197 13 826 A1 and from U.S. patent Document U.S. Pat. No. 6,075,636 respectively. A light-beam generating device for generating a parallel light beam, a scanning unit for generating a scan pattern by deflecting the parallel light beam over a defined angular range, and a detector unit for detecting the light reflected by the object are provided in these documents. In this case, the scanning unit contains a rotating polygonal mirror with several reflecting partial mirror surfaces.
The present invention relates to a system for the optical detection of a remote object for monitoring the air space situated in the flight direction in front of an aircraft, such as a helicopter, with respect to poorly recognizable obstacles, such as overhead lines or wire cables. In order to detect poorly recognizable and therefore poorly reflecting objects over distances of a typical magnitude of 500 m in this application, the light energy delivered by the scanning unit cannot be distributed over the entire defined angular range but has to be kept as compact as possible and should have the highest possible intensity.
When a rotating polygonal mirror is used, the problem arises that, during each impingement upon an edge separating two adjacent partial mirror surfaces, the light beam is split into two parts which leave the scanning unit in two different directions. This leads to a considerable reduction of the intensity of the emitted parallel light beam. Although the relative effect of this loss can be reduced by enlarging the diameter of the polygonal mirror compared with the diameter of the parallel light beam, this would result in very large polygonal mirrors which are difficult to handle.
It is an object of the invention to provide a system for the optical detection of a remote object which has a high capacity. In particular, the system is to permit the optical detection of remote objects, such as poorly recognizable obstacles in the air space in the flight direction in front of an aircraft.
As a result of the invention, a system is created for the optical detection of a remote object, having a light beam generating device for generating a parallel light beam, a scanning unit for generating a scan pattern by deflecting the parallel light beam over a defined angular range, and a detector unit for detecting light reflected by the remote object, the scanning unit containing a rotating polygonal mirror with several reflecting partial mirror surfaces. According to the invention, the light beam generating device for generating a parallel light beam is provided in two different beam positions which, in response to a rotating position indicating signal indicating the rotating position of the polygonal mirror, can be changed over from one partial mirror surface to an adjacent partial mirror surface.
The light beam generating device is preferably provided for generating a parallel light beam in two different beam positions mutually offset in parallel.
According to an embodiment of the invention, the light beam generating device can contain two light sources for generating the parallel light beam in the two different beam positions.
According to another embodiment of the invention, it is provided that the light beam generating device contains a light source, and that a beam position switching unit is provided between the light source and the scanning unit, for changing over the beam position of the parallel light beam from one partial mirror surface to an adjacent partial mirror surface in response to the rotating position indicating signal indicating the rotating position of the polygonal mirror.
According to an embodiment thereof, it is provided that the beam position switching unit has the following successively arranged in the beam path: A polarizer for generating polarized light of a defined polarization condition from the light emitted by the light source; a Pockels cell for changing over the polarization condition of the light emitted by the polarizer between a first polarization condition and a second polarization condition, as well as a first polarization beam splitter for scattering the light having the first polarization condition in a first beam position in which the parallel light beam impinges on the one partial mirror surface, and for scattering the light having the second polarization condition in a second beam position, in which the parallel light beam impinges on the adjacent partial mirror surface.
The polarizer preferably contains a second polarization beam splitter with a λ/2-plate connected on the output side, for generating the polarized light of a defined polarization condition.
The first polarization beam splitter preferably contains one λ/4-plate respectively in the beam path of the light having the first polarization condition and in the beam path of the light having the second polarization condition, for generating the parallel light beam by means of circularly polarized light.
According to an embodiment of the invention, it is provided that the scanning unit contains the rotating polygonal mirror for deflecting the parallel light beam in a first direction and, in addition, a swivelling mirror for deflecting the parallel light beam in a second direction.
Preferably, the polygonal mirror is provided for deflecting the parallel light beam in the horizontal direction, and the swivelling mirror is provided for deflecting the parallel light beam in the vertical direction.
The detector unit preferably contains a detector and a lens system provided for imaging the light reflected by the distant object on the detector.
The detector preferably is a site-resolving detector.
According to an embodiment of the invention, the detector is a one-dimensional detector.
According to an embodiment of the invention, it is provided that the detector has a spherical or cylindrical image area.
Preferably, a swivelling mirror is provided in the beam path of the light reflected by the distant object in front of the detection unit, for adapting the direction of the light received by the detector unit to the direction of the light emitted by the scanning unit.
Preferably, the swivelling mirror provided for adapting the direction of the light received by the detector unit to the direction of the light emitted by the scanning unit is the same swivelling mirror which is provided for deflecting the parallel light beam in the second direction.
According to an embodiment of the invention, the lens system of the detector unit is a lens system of the double Gauss type with high precision and luminous intensity.
The system according to the invention is preferably used for monitoring the air space situated in the flight direction in front of the aircraft with respect to poorly recognizable obstacles, such as overhead wires or wire cables.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.